Sports Stats ‘on Tapp’ is a sports statistics blog published with a focus on stats that go beyond the numbers.

Heading into the last four weeks of the NFL regular season, four teams have stopped their opponents’ offenses from scoring in 70 percent or more of their possessions. Topping the list is the San Francisco 49ers defense, which has 94 stops in 129 possessions, a 74.6 STOP Factor.

The other three teams are: Houston (74.0 percent), Chicago (73.0 percent) and Arizona (72.2 percent). This is the third consecutive week that the 49ers defense has held the number one spot in these rankings.

If we look at the rankings after Week 9, we see that several teams have amped up their defensive efforts in the last month while others have seen their defenses drop in the rankings. The biggest gainers since Week 9 have been the Cincinnati Bengals who have jumped from 22nd in the rankings to a Top 10 spot at number 10, a gain of 12 spots. The Denver Broncos have jumped from 14th to sixth (a move of eight posts), and the Pittsburgh Steelers have gone from 18th four weeks ago to 11th this past week.

Two teams, Miami and Philadelphia, have seen the biggest drops in their rankings in the last four weeks. Miami has gone from seventh to 14th, while the Eagles have dropped from 17th to 24th, both a loss of seven spots.

(The STOP Factor is based on the premise that it is the defense’s job to stop their opponents from scoring on each possession. To get a team’s STOP Factor, you divide the number of times a defense stops the offense from scoring – offensive unit TD or field goal – by the number of total possessions by the opposition.)

Following is each NFL teams’ STOP Factor. Listed is how many times each team stopped the opponents from scoring, the number of possessions their opponents had, and the percentage of possessions that each team prevented the other team from scoring (stats are through Week 13 games).